While it is evident that the gonads secrete substances which inhibit gonadotropin release by the pituitary gland, there is considerable room for improved precision in the identity of the circulating inhibitory substance(s). Both very old and very recent data suggest that non-steroidal compounds may contribute to this inhibition and we will attempt to demonstrate such non-steroidal inhibition in animals with ovarian or testicular tissue implanted in the omentum and/or spleen. More importantly, we will use animals with steroids implants in the omentum to determine whether metabolites of estrogens or androgens might be producing effects previously attributed to a non-steroidal "Inhibin". Other studies will continue the quantitative assessment of the effects of various steroid implants on gonadotropin secretion (and, through collaborative efforts, on sexual behavior) both in the intact and the castrated rat. Ultimately, the purpose of these studies is to better understand the effective contributions of the various steroids (and non-steroids) which circulate as a result of the gonadal secretory process.